<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>元素选择器</title>
    <script src="../jquery-3.4.1.js"></script>
</head>
<body>
<div class="a">
    <p>class="a"</p>
    <p>选中</p>
</div>
<div class="imooc">
    <p>class="imooc"</p>
    <p>选中</p>
</div>
<div class="imooc1">
    <p>class="imooc1"</p>
    <p>选中</p>
</div>
</body>
<script type="text/javascript">
    $("p").css("background","green");
</script>
</html>